ABSTRACT Alcohol dependence is a chronic relapsing disorder characterized by compulsive alcohol use and deficits in cognitive and executive functions. The emerging picture of alcohol addiction is that of a disease of disrupted control and compulsion, rather than merely of the pursuit of pleasure. Indeed, alcoholic patients exhibit deficits in cognitive functions governed by prefronto-cortical regions of the brain; these impairments manifest as increased risk taking, poor decision making, and loss of inhibitory control and they are thought to promote further excessive drinking. While evidence shows that chronic alcohol exposure results in loss of behavioral control, little is known about how neurotransmitter systems in prefronto-cortical regions are adversely impacted by alcohol and how they contribute to the susceptibility to drink excessively. This project, to be conducted at Boston University in the rich neuroscience community of Boston, concerns Sigma-1 receptor (Sig-1R), a molecular chaperone highly expressed in the central nervous system. We have shown that blockade of Sig-1R reduce excessive drinking in animal models of alcoholism, while they do not reduce responding for ethanol in control rats or the intake of sweet solutions. We have also found that activation of Sig-1R increases the reinforcing efficacy of alcohol, inducing binge-like drinking. Sig-1Rs are highly expressed in the prefrontal cortex, a brain area which normally exerts ?top-down? inhibitory control over behavior; importantly chronic intermittent alcohol causes a dramatic up-regulation of Sig-1R protein in prefrontal regions, suggesting that hyperactivity of this system may have a key role in excessive drinking and in the neuroplasticity observed in alcohol addiction. The central hypothesis of this proposal is that hyperactivity of Sig-1R in prefronto-cortical regions mediates the chronic alcohol-induced high susceptibility to drink excessively. A secondary hypothesis is that these neuroadaptations of the Sig-1R system mediate chronic alcohol-induced cognitive deficits and the long-lasting modifications of prefronto-cortical glutamatergic transmission and dendritic spines. Aim 1 will identify changes in Sig-1R levels associated with ethanol-dependence and ethanol drinking, and will determine whether Sig-1R in prefronto-cortical areas mediates excessive alcohol intake and motivation to drink. Aim 2 will determine whether Sig-1R mediates chronic alcohol-induced alterations in cognitive function, synaptic glutamate NMDA receptor expression, and dendritic spines in prefronto-cortical areas. If the aims are achieved, our understanding of the neurobiological adaptations driving excessive alcohol intake would significantly increase and new avenues of investigation towards the pharmacological treatment of alcohol use disorders would open.